Coffee is widely recognized for its caffeine content and its ability to promote alertness. However, it represents much more than just caffeine dissolved in hot water; it is a chemically complex plant extract that contains hundreds of bioactive compounds capable of generating various effects, surprising or beneficial, even when consumed in decaffeinated form.
Among the most peculiar effects listed, one study points out that approximately three in ten individuals report feeling the need to evacuate shortly after consuming coffee, a phenomenon that occurs rapidly with both regular and decaffeinated coffee, indicating that it is not limited to caffeine, although the exact compounds responsible remain unknown.
Morning coffee consumption can make the colon more active. Furthermore, what is added to the drink can influence bowel transit; lactose present in milk or certain sugar substitutes can stimulate the intestines, especially in large quantities.
In some people, coffee has the potential to intensify symptoms of reflux, a condition where stomach acid returns to the esophagus. This reflux can manifest beyond heartburn, contributing to coughing, chest wheezing, and other respiratory issues by affecting the throat and airways.
Caffeine can temporarily raise intraocular pressure in individuals with glaucoma or ocular hypertension, conditions that already involve elevated eye pressure, making it crucial to control this pressure to protect the optic nerve. For this reason, some people with these conditions may receive recommendations to moderate their coffee and caffeine intake.
There is also an auditory condition characterized by the Eustachian tube remaining abnormally open, allowing one to hear their own voice or breathing at a high volume. People with patulous Eustachian tube dysfunction are occasionally advised to reduce caffeinated beverages and stay hydrated, as dehydration can worsen symptoms, although there is little direct evidence that coffee is the cause of this condition.
The interaction between caffeine and migraines is complex: while caffeine can help relieve attacks, excessive consumption or abrupt cessation of the habit can, paradoxically, trigger an episode in some cases.
Coffee also demonstrates the ability to modify the effectiveness of certain medications. For example, it can decrease the absorption of drugs such as levothyroxine (for thyroid) and alendronate (for osteoporosis). Additionally, caffeine can slow down the metabolism of the antipsychotic clozapine, increasing its blood concentration.
In some scenarios, it is the drugs that alter the action of coffee. One example is the antibiotic ciprofloxacin, which decreases caffeine metabolism, causing habitual coffee to remain in the body longer.
Diterpenes present in coffee, specifically cafestol and kahweol, have the potential to increase total cholesterol and LDL ('bad' cholesterol). However, short-term studies indicate that these same compounds can reduce lipoprotein (a), suggesting a potentially lower risk of heart attack or stroke.
Other components, such as chlorogenic acids, can promote a modest reduction in blood pressure and improve vascular function. Thus, the overall impact of coffee on cardiovascular markers is not yet fully understood.
Moreover, laboratory experiments suggest benefits for gut bacteria. Some chlorogenic acids are not absorbed in the small intestine, reaching the colon where they are decomposed by bacteria. Complex carbohydrates and melanoidins, byproducts of roasting, also reach the colon, being fermented by the gut microbiome.
Although small human studies suggest that coffee consumption can modify the composition of the gut microbiome, the evidence is still under development, making it premature to classify it as probiotic.
Coffee can also restrict the absorption of iron from food. Consuming coffee during a meal can significantly reduce the absorption of non-heme iron, found mainly in vegetables. This occurs due to polyphenols, including chlorogenic acids, which bind to iron in the digestive tract, hindering its assimilation. This issue is more relevant for those who already have low iron levels or rely on vegetable sources.
Coffee stimulates parts of the digestive system even in the absence of food, potentially triggering the release of trypsin, a pancreatic enzyme essential for protein digestion, in both regular and decaffeinated coffee. It is not defined whether this digestive stimulation alters the perception of hunger.
Additionally, coffee can influence intestinal hormones related to satiety and appetite, but studies have not consistently confirmed whether this leads to eating more or less.
Although caffeine and increased alertness are the most noticeable characteristics of coffee, the reality is much broader. A single cup contains hundreds of substances that interact with the digestive system, the microbiome, medications, and nutrients, often in unexpected and complex ways.